1) The knight you are jumping over must belong to one of your opponents (ein fremd Ritter).2) The knight you are jumping over may be on any level.3) The field your knight is landing must be on the same level, up 1 level or down any number of levels. Note: The rules do not say that the field the knight is landing must empty, but it is obvious that it must be free as you can't land on any knights.4) The knight may only jump orthogonally.

A person at BGG says you can, but it may depend on the language of the rule or the version, not really important if it is decided and well known

Here on BàJ, the help text on the card is different in french and in english, that's the important thing, this should be easily fixed"Un de vos chevaliers saute par dessus un chevalier adverse. Le chevalier se déplace en ligne droite et peut monter d'un niveau au maximum."

"Move one of your knights past one other knight by jumping over it. The knight must move in a straight line orthogonally. In moving, the knight may move up one level or down any number of levels."